Conventionally, with respect to solid-liquid interfaces, in academic, the concept of a contact angle which was used to express the wettability of a liquid with respect to a solid surface was slightly known in the literature, and it can be said that almost no other evaluable research reports existed. On the other hand, in industry, since an increase in the cleanliness of a solid surface has been strongly desired in magnetic film technology for recording and in liquid crystal technology for flat screen displays, it can be said that a resolution of the solid-liquid interface problem will become progressively essential.
Hereinbelow, the solid-liquid interface problem will be discussed in the context of the most typical surface contamination and removal of surface contamination sources, using semiconductor technology as an example.
In semiconductors, there are three representative sources of surface contaminants: particles (hereinbelow, the term "particles" will include the so-called debris), metallic elements, and organic molecules. If the surface of a semiconductor is contaminated by any of these, the yield of acceptable products in semiconductor device production, and the reliability of the finished products, decreases markedly. Accordingly, in semiconductor manufacturing processes, technology for the cleaning of semiconductor substrate surfaces has been developed, and chief among such technologies are wet washing technologies utilizing chemicals or ultra-pure water.
Here, in this wet washing technology, aqueous ammonium peroxide (NH.sub.4 OH--H.sub.2 O.sub.2 --H.sub.2 O) is used in the removal of particles or metallic elements from a semiconductor substrate surface, aqueous hydrochloric peroxide (HCl--H.sub.2 O.sub.2 --H.sub.2 O) is used in the removal of metallic elements, and furthermore, aqueous sulfuric peroxide (H.sub.2 SO.sub.4 --H.sub.2 O.sub.2 --H.sub.2 O) is used in the removal of primarily organic materials.
Then in the final stage of this wet cleaning, the thin natural oxide film which is formed on the substrate surface is removed using dilute hydrofluoric acid (HF--H.sub.2 O), and the chemicals and like remaining on the substrate surface are removed using ultra-pure water.
However, in this wet cleaning technology in semiconductor manufacturing, the quantized effects of the mutual interaction of ultra-pure water and chemicals (liquids) with the semiconductor (solid) surface were not known with respect to the problem of the ease of precipitation of, for example, impurities, such as particles or metallic elements, onto a solid surface, so that the effects of various types and amounts of impurities such as particles or metals or the like contained in a solution of ultra-pure water or chemicals (dilute hydrofluoric acid, aqueous hydrochloric peroxide, aqueous ammonium peroxide, aqueous sulfuric peroxide, and the like) on the cleanliness of a semiconductor surface, and the relationship between the semiconductor surface and the unavoidable contamination by these impurities, were not sufficiently clear.
In other words, it has not been made clear to what extent the cleanliness of the semiconductor is possible even if cleaning chemicals are initially employed. For this reason, at semiconductor manufacturing facilities, the management of chemicals, for example, the decision as to after what period to replace the chemicals has been conducted solely on the basis of trial and error, and this is unsatisfactory from the point of view of industrial productivity.
The present invention solves the problems present in the conventional technology described above; it has as an object thereof to provide a method and an apparatus for evaluating a segregation at a solid-liquid interface which is capable of specifying and measuring quantitatively a substance (hereinbelow referred to as a "segregation substance") which precipitates preferentially onto a solid surface from a solution of ultra-pure water or chemicals or the like, or which, on the contrary, remains preferentially in a solution of ultra-pure water or chemicals or the like (or which elutes into the liquid from the solid surface).